Conventional methods known in the art for producing silicon oxide powder include a method in which a silicon dioxide-based oxide powder is heat treated in a non-oxidating atmosphere under reduced pressure to generate silicon monoxide vapor, and this silicon monoxide vapor is condensed in gas phase to continuously produce a minute amorphous silicon oxide powder of up to 0.1 μm (JP-A 63-103815: Patent Document 1), and a method in which a silicon starting material is heated for evaporation, and the vapor is deposited on the surface of a surface roughened substrate (JP-A 9-110412: Patent Document 2).
At present, silicon oxide powder is expensive, and further reduction in cost is required if it is to be used for a cathode active material of lithium ion secondary battery. For the cost reduction, improvement in yield and productivity by increasing the reaction speed is effective.
However, the typical conventional methods as described above used in producing the silicon oxide are not the methods primarily developed by taking the cost reduction into consideration, and the means that can be used for increasing the reaction speed is not clearly indicated.